Advertisements are sometimes intended for a particular group or demographic of potential consumers. Targeted advertisement in the context of subscription television (e.g., cable or satellite) is often inserted by a user's set-top box (STB) into advertising slots in a live Moving Picture Experts Group (MPEG) transport stream. Often a head end may control which set-top box plays a particular ad. Protocols often claim to be “privacy preserving” because the set-top box makes the selection decision, and the private information used to make that decision may be contained in the STB, rather than at the cable/broadcast head end. However, in such an arrangement private information may be inferred from the communication between the STB and the head end during the processes of (1) selecting households to play an ad and (2) counting the number of times the ad was presented by these STBs.
One protocol for targeted advertising, in which households are selected by the head end to play an ad, is as follows. An ad campaign is provided to the cable/broadcast head end from some external source (such as media buyer or advertiser). That ad campaign has an associated set of criteria that describes the desired viewers (e.g., households with net income greater than $100,000, or families with preschool children) and a total number of households to reach. Each STB contains information about its household (e.g., net income). When an opportunity to show an ad is approaching, the head end sends an “ad opportunity” message to all STBs, where the message contains an identifier for the advertisement (the contents of the ad may be pushed to the STB separately) and also contains the criteria for showing that ad.
The STBs use the household's private information to evaluate the criteria for a match. If there is a match, the STB sends a “criteria met” message to the head end, identifying that STB. The head end selects a subset of the households from those that responded (the subset corresponding to the number of households that need to be reached), and sends a “show ad” message to each selected STB, requesting that the ad be shown. The ads will be locally stored on the STB hard disk (HD) in advance, and shown locally from the HD. To minimize overhead, a distributor of the ad can push ad files onto the STB during low-traffic periods (e.g., in the middle of the night) when bandwidth is least utilized. After the ad is shown, an “ad shown” message is sent from the STB to the head end, allowing the individual showing of the advertisement to be counted. This is necessary in order to verify that the ad has been shown to the required number of households.
While the above protocol does not require the user's specific private information to leave the STB, the “criteria met” message does inform the head end (any other party who can access this message) that a specific STB meets specific criteria. While explicit private information (e.g., the exact household net income) is not sent from STB to the head end, by sending the “criteria met” message, the STB is providing private information about its specific household to the head end (e.g., by stating that the household meets the criteria, the STB is indicating to the head end that this household's net income is greater than $100,000, for example). Therefore the conventional protocol still reveals sensitive information.
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